1. Field of the Invention
The present invention relates to an amplitude control device for automatically controlling the amplitude of a digital signal and, more particularly, to an amplitude control device for a digital signal comprising an amplitude reference signal component time-base multiplexed thereto.
2. Description of the Prior Art
An automatic gain control device is often used to obtain the correct amplitude in a digital signal resulting from analog/digital (A/D) conversion of an analog signal such as a video signal. The most common automatic gain control method used during A/D conversion is a feedback control method whereby an amplitude reference signal is time-base multiplexed to the input analog signal and referenced to obtain the specified signal amplitude in the output digital signal.
There are two primary signal amplitude control methods: directly controlling the signal amplitude before A/D conversion using a variable gain analog amplifier; and controlling the digital signal after conversion by regulating the reference voltage of the A/D converter to vary the input dynamic range of the A/D converter.
There are drawbacks to each of these known methods, however. With the former method, the analog variable gain device must be adjusted after assembly to assure correct operation. With the latter method the signal to noise (S/N) ratio deteriorates because the dynamic range of the A/D converter is used at a less than optimum band width.